(1) Field of the Invention
The present invention relates to a process for producing a ring-substituted arene borane which comprises reacting a ring-substituted arene with an HB organic compound in the presence of a catalytically effective amount of an iridium or rhodium complex with three or more substituents, excluding hydrogen, bonded to the iridium or rhodium and a phosphorus organic ligand, which is at least in part bonded to the iridium or rhodium, to form the ring-substituted arene borane. The present invention further relates to compounds for catalyzing the process comprising an iridium or rhodium complex with three or substituents, excluding hydrogen, bonded to the iridium or rhodium and optionally, a phosphorus organic ligand, which is at least in part bonded to the iridium or rhodium.
(2) Description of Related Art
Alkyl and arylboronic esters and acids are versatile alkyl and aryl transfer reagents in organic chemistry wherein the boron serves as a “mask” for a broad range of heteroatoms and functional groups. Some of the most remarkable and broadly used applications of organoboron chemistry are catalytic cross-coupling reactions of C—B and C—X (X=Cl, Br, or I) groups which yield new C—C bonds as shown below. In the pharmaceutical industry, organoboron complexes are key building blocks for drug manufacturing, versatile reagents for high-throughput parallel synthesis in drug discovery, and exhibit some useful and unique biological activities.
Arylboronate esters and the corresponding acids are presently prepared by reacting Grignard reagents generated from halogenated aromatics and magnesium metal with alkyl borate reagents. A related method involves the reaction of alkyllithium reagents with aromatic halides or arenas to generate lithium reagents which are subsequently reacted with alkyl borates. Significant limitations of the current technologies include: (1) the reactions are run in ethereal solvents, (2) halogenated aromatics must be synthesized from hydrocarbon feedstocks, (3) for large-scale synthesis, unreacted chlorinated aromatic starting materials and biaryl byproducts can create significant environmental hazards and pose waste disposal problems, (4) in some instances attempted product isolation has resulted in explosions attributed to unreacted lithium and magnesium intermediates, (5) Grignard and organolithium reagents can be incompatible with a range of common functional groups including esters, amides, bromides, chlorides, iodides, alcohols, acids, and the like, and (6) cryogenic cooling is sometimes required to prevent side reactions.
In light of the above limitations of the current processes for producing boronate esters and acids, there remains a need for a general synthetic route to synthesizing boronate esters and acids which does not have the limitations of the current processes.